I am not a synthetic kind of guy.I have a 92 4x2 with 249k that I bought with 12k and has never had synthetic and runs great.My 4runner has 260k plus without synthetic and I just gave my Mom my 90 LS400 with 270k thats never had synthetic as I got an 05 IS300.I would run it in my trannys and diffs but really don't see the need to spend the extra money for the engine.I just change my oil and filter.